Tech changed AC fan speed. Does this sound correct?

[philw]

I was out of town last week. We are in our 2nd summer in this house and I never thought the AC worked well last summer so I called a service company. I was out of town last week when they arrived. (We have two systems. The one for the upstairs cools well with 56 degree air coming out at outside temps of 80 degrees. Ot main floor unit barely keeps up if it is over 90 degrees outside and falls behind if a lot of traffic goes in and out of the house. I also note at any given time the air coming out of the vents on the main floor is 4-5 degrees warmer than the upstairs unit.) I also notice at any given time when both units are running the suction side of the upstairs system is much colder that the main floor unit. My wife had the guy talk to me when he was ready to leave and he said this. He suspected the fan speed was too high to properly exchange the heat from the house to the evaporator so he lowered the fan speed to the 2nd of 4 speed settings. (It was on high or 4) I will agree the air at the vents are cooler now, just wanting to know if this is a productive action to take? I have always noted a system fan runs much faster when cooling in the summer than heating in the winter and assume there is a reason for this.

[Shophound]

Is your system doing a better job of keeping your first floor comfortable since the fan speed was changed?

The reason behind the blower speed change between heating and cooling operation: cold air is more dense than hot air, so it requires more fan power to deliver the correct amount of air to the supply vents. The cooling coil also needs a certain amount of air moving over it to keep the coil from freezing, and to assure good exchanging of heat between the air and the coil. Move the air too fast...coil can't take out as much heat. Move the air too slow, the coil takes out too much heat and begins to freeze the moisture that collects on the coil when the system is running.

[dash]

He could be right and a very good tech,or he could be wrong, wait and see.

[beenthere]

He could be right and a very good tech,or he could be wrong, wait and see.

yea. Can't tell from our side of the internet what he found.

Time will tell.

[philw]

Any advice on what to watch for other than "how does it feel"? He did note that he achieved a increase of 2 degrees in temp drop from the return to the supply side of the evap. in doing this and now has a 20.1 degree temp drop. Does that sound functional? Lastly, should I not press them to get my 3.5 ton main floor unit to have similar suction side line temp feel as th 1.5 ton 2nd floor system? My cousin who does Apartment maint. work said rule of thumb is "beer can cold" to the touch on the suction side. The upstairs unit is, the main floor is not yet.

[Twilly]

Twilli says he done good, maybe

[beenthere]

If your humidity is higher on the first floor, then the line won't be as cold.

Maybe you should have your cousin check it.

[Shophound]

Any advice on what to watch for other than "how does it feel"? He did note that he achieved a increase of 2 degrees in temp drop from the return to the supply side of the evap. in doing this and now has a 20.1 degree temp drop. Does that sound functional? Lastly, should I not press them to get my 3.5 ton main floor unit to have similar suction side line temp feel as th 1.5 ton 2nd floor system? My cousin who does Apartment maint. work said rule of thumb is "beer can cold" to the touch on the suction side. The upstairs unit is, the main floor is not yet.

What I meant by (cue Bob Dylan voice) "how does it feel" was definitely NOT "beer can cold". Anyone telling you that is their metric for determining a system's performance needs deeper HVAC education. No offense here, but your cousin is in a realm where a lot of bad info about a/c repair circulates...I used to be in that realm and had to undergo some rude awakenings to become better informed.

What I mean by "how does it feel" is since the tech changed the blower speed, are you now comfortable. The end goal of air conditioning is indoor human comfort in adverse outdoor weather. If his tweak got you there, you're probably okay. It's up to the tech to sweat the technical details, that is what you're paying him for. If he hasn't won your confidence, is it based on you still not being comfortable downstairs?

[machery]

Makes sense, assuming that it is a gas or oil furnace, every one I have seen came from the factory with the cooling fan speed set on high, it being up to the installer to properly set the cooling speed in relation to the tonage of the unit. Just about every furnace I find has the cooling speed on high regardless of the unit size

[cmajerus]

20 degrees is typically a good TD, most likely he set the blower where it should have been set at system startup(rarely happens that high is proper for cooling in the northern states) I have alot of systems that the heating speed is higher than the cooling speed. Beer can cold is a good way to shorten the A/C life expectancy. It may have been accepted yrs ago(still wasn't proper) but todays systems cannot be diagnosed this way.

[philw]

We have had a cool spell down to the low 60's at night. Heat/ humidity load is not that high even during day lately. Will need to wait for it to heat up toward the end of the week. I will post back later.